Electron multiplier tube



Jan. 9, 1951 c. F. MILLER ELECTRON MULTIPLIER TUBE Filed Feb. 25, 1949UUUUUUUU INVENTOR. C'A/PL F M440? BY fi fiTTOP/Vi') Patented Jan. 9,1951 ELEGTRON MULTIPLIER TUBE Carl F. Miller, Summit, N. J assignor toNational Union Radio Corporation, Orange, N. J a corporation of DelawareApplication February 25, 1949, Serial No. 78,311

This invention relates to electron discharge tubes, and moreparticularly to electron multiplier tubes utilizing a secondaryelectron-emissive electrode or dynode.

A principal object of the invention is to provide an improved dynodeconstruction for secondary electron-emission tubes.

- Another object is to provide an improved secondary electron multipliertube. A feature of the invention relates to a dynode for secondaryelectron-emission tubes, which dynode is of large area and open-workconstruction, as distinguished from the usual fiat-platedynodeconstruction.

Another feature relates to a secondary electron-emissive dynode which isin the form of a wire-wound grid having the windings of predeterminedpitch and wire thickness, and oriented with respect to the primaryelectrons so as to translate efiiciently incident primary electrons intoreleased secondary electrons.

Another feature relates to a secondary electron-emissive dynode in theform of a wire-wound grid for surrounding the anode or electroncollector.

A further feature relates to the combination of a source of primaryelectrons, a secondary electron collector electrode, and awire-wound-grid dynode between the said source and collector,

the dynode being shaped and dimensioned so as r to interceptsubstantially all the primary electrons before they reach the collector,while allowing the greater part of the released secondary electrons tomove to the collector.

A still further feature relates to the novel organization, arrangement,and relative location and proportioning of parts which cooperate toprovide an improved electron multiplier tube.

Other features and advantages not specifically enumerated, will beapparent after a consideration of the following detailed descriptionsand the appended claims.

In the drawing, which shows certain preferred embodiments,

Fig. 1 is a top plan view, partly sectional, of an electron multipliertube according to the invention.

Fig. 2 is a cross-section l view of Fi 1, taken along the line 2-2thereof and viewed in the direction of the arrows.

f, Fig. 3 is a sectional view of Fig. 2, taken along the line 3-3thereof.

Fig. 4 is a view similar to that of Fig. 2, but showing a modifiedconstruction of the dynode and collector electrode.

12 Claims. (Cl. 250-174) Fig. 5 is a sectional view of Fig. 4, takenalong the line 5-5 thereof.

Fig. 6 is an elevational view of a modification of the tube of Fig. 1.

Fig. 7 is a cross-sectional View of Fig. 6, taken along the line '!1thereof.

Fig. 8 is a composite structural and circuit diagram showing a typicaloperating circuit for the tube according to the invention.

Referring to Fig. 1, there is shown an evacuated bulb or envelope of anysuitable well-known construction.

Mounted within the highly evacuated bulb I, is an electron-emittingcathode 2 which is adapted to be raised to electron-emitting temperatureby any suitable heater element of filament (not shown). Surrounding thecathode 2 is any wellknown helically-wound wire grid 3 which issupported by the usual grid side rods 4, 5. Likewise surrounding thecontrol grid 3 is a shield grid 6 Which may consist of a helically-woundwire attached to the usual grid side rod supports 1, 8. Surrounding thecathode and two grids is a .curved metal plate 9 which acts as adeflector for the primary electrons emitted from the cathode Z, causingthem to follow electron trajectories represented by the dotted lines inFig. l. Mounted in spaced relation to the cathode and double gridassembly described above, is a dynode consisting of a helically-woundwire grid I!) which is wound around and attached to a pair of gridsiderods lid and Ill). Suitably mounted within this dynode grid is aflat metal anode 12 which acts to collect the secondary electronsreleased from the dynode grid l0. Located between the dynode grid andthe shield grid 6 is a channeled metal baiiie plate l3. As shown in Fig.1, the plate l3 has its concave side facing the cathode 2, and it issuitably dimensioned and energized by an appropriate potential as is thedeflector plate 9, so as to cooperate therewith in constraining theprimary electrons from cathode 2 to follow the electron trajectoriesrepresented by the dotted lines. The baflie l3 also positively preventsatoms of the cathode coating, e. g., barium or strontium, or otherparticles emanating from the cathode, from contaminating the coatedsurface of dynode Ill. The bulb I has the usual lead-in wires or contactprongs (not shown) connected to the respective electrodes asschematically shown in Fig. 8. i

In accordance with one feature of the invention, the dynode grid Ill isformed of comparativelv heavy wire stock, and the pitch (i. e. the

number of turns per inch) and the wire diameter of the wire H] aredesigned so as to have a predetermined relationship to the angle a. Theangle a. represents the angle between the trajectories of the primaryelectrons and the longitudinal axis of the dynode grid, as indicated inFig. 3. By correlating the said pitch and wire diameter with the angleof approach of the primary electrons, it will be seen that each gridwire acts as a shield for the next adjacent grid wire, in so far aspreventing the direct access of the primary electrons to the collectorI2 is concerned. In other words, the primary electrons strike the wiresIE3 at such an angle that substantially all these primar elec-v tronsfollowing the trajectories, as shown in the. drawing, must strike thedynode ill. The dynode It] may be formed of a metal which has a highcoeiiicient of release of secondary electrons in response to impingingprimary electrons of predetermined velocity. If desired, the wire It canbe coated with any material well-known in the art which has a highcoefficient of secondary electron emission. The released secondaryelectrons from the individual turns of the dynode grid followtrajectories represented by the arrows l (Fig. 3), and since thecollector electrode I2 is at a higher positive potential than the dynodegrid, these secondary electrons are capable of moving freely to thecollector electrode.

By this arrangement it is possible therefore, to

provide the dynode grid with an efiiciently large area, while positivelypreventing direct bombardment of the collector electrode by the primaryelectrons. Thus, the dynode and collector electrode are protectedagainst deposition of cathode material thereon, and the bafile i3 anddynode grid can be run at a lower temperature than is possible withprior constructions since both the collector and dynode grid areprotected from the direct heat of the cathode. Thus vaporization of thedynode surface coating is greatl reduced as compared with priorconstructions.

It will be seen that for larger angles of a, correspondingly largecross-sectional wire should be used for the grid H), or the pitch of thegrid windings of the dynode can be increased so as to prevent theprimary electrons from cathode 2 from striking the collector [2. Withthe foregoing construction, it is possible to have extremely smallspacing between the collector l2 and the dynode windings. For example,spacings as little as .002 inch have been found practicable, thus makingthe electrode l2 a very efiicient collector of the secondary electrons,particularly if the direct current positive voltage applied to electrodeI2 is high enough to reach through the space between adjacent dynodeturns.

In those cases where low electrostatic capacity is required between thedynode and the collector, instead of making the collector in the form ofa single sheet or plate as above described, it can be made of individualspaced wires or rods. Thus as shown in Figs. 4 and 5, the dynode l5 mayconsist of a helically-wound wire attached to a pair of grid supports16, ll. Fig. 4 shows the dynode grid substantially rectangular in shape,although this is not necessary. The collector electrode consists of aseries of spaced wires or rods l8 which are mounted between a pair ofparallel channel members I9, 20, to which the wires l8 can be suitablyfastened, for example by welding. The wires I8 are preferably inclinedso as to have a pitch identical with the pitch of the grid l5, and theWires I8 likewise preferably have a cross-sectional size approximatelyequal to the spacing between adjacent turns of the grid l5, it beingunderstood that the said wires l8 are located preferably in alignmentwith the said grid-turn spacings. In this embodiment, the trajectoriesof the primary electrons are represented by the arrows 2|, and the angleof incidence of these primar electrons with respect to the dynode gridturns, is represented by the angle a. The trajectories of the secondaryelectrons are represented by the curved arrows 22. Here again thecross-sectional size of the wire from which grid I5 is formed, issufiiciently large and the pitch of the grid turns is chosen so thatwith respect to the trajectory of the primary electrons, each grid turnacts as an efficient barrier to prevent primary electrons from directlyreaching the collector.

In both the foregoing embodiments, the collector electrode is shown asbeing surrounded by the dynode grid. Figs. 6 and 7 show a modificationwherein the collector electrode is in the form of a tubularorcylindrical metal plate 23 which surrounds the dynode grid 24. Thisdynode grid 24 can be similar to grid ill or grid [5, and is in the formof a wire helically wound around and attached to a pair of grid supportrod 25a, 25b. The remaining electrode elements of Fig. 6 can beidentical with those of Fig. 1, and may comprise, for example, a cathodesleeve 26 having its end portion provided with a coating 2! ofelectron-emissive material. The sleeve 25 may be provided with anysuitable heater element 28 for raising it to emitting temperature. Acontrol grid 29 is mounted in spaced relation to the cathode, and ashield grid 39 is mounted in spaced relation to the control grid. Anelectron baflle 3| is mounted in spaced relation to the shield grid. Apair of electron deflector plates 32, 33, are provided for causing theelectrons to follow the desired trajectory towards the dynode 24, asrepresented by the dotted arrows. The secondary electrons released fromthe dynode are attracted to the collector 23 along trajectoriesrepresented by the curved arrows 34. It will be noted, therefore, thatthe electron trajectories impinge upon r the internal peripheries of thesuccessive turns of the grid 24, and the cross-section of the wireforming the grid 24 is sufliciently large, and the pitch is chosen sothat for the desired angular approach or trajector of the primaryelectrons, each grid turn effectively shields the succeeding grid turnagainst the passage of the primary electrons directly to the collector23.

8 shows a typical circuit arrangement in which the tubes of theforegoing embodiments may be employed. A suitable input signal source 35is coupled through a tuned input 38 across the control grid 3 and thecathode 2. The shield grid 4' is connected to any suitable positivedirect current potential represented schematically by the battery 3?.The deflector 9 can then be connected to a suitable potential tap on thesource 3?, to cause the primary electrons to follow the desiredtrajectory. If desired, the baille l3 can also be connected to this samepotential. The dynode grid to is connected to a suitable high potentialtap on the source 3'5, and the collector electrode i2 is conn ctedthrough a resistor 38 to another point on the source 3'! which is ofhigher potential than the point to which the grid I0 is connected. Thesignal developed across resistor 38 can be coupled through a suitablecoupling condenser 39 to any desired load or utilization circuit.

Various changes and modifications may be made in the disclosedembodiments without dew parting from the spirit and scope 'of thinvention.

What is claimed is:

1. An electron tube, comprising means to develop a beam of primaryelectrons, a secondary electron collector, and a dynode upon which saidprimary electrons impinge to release secondary electrons, said dynodebeing in the form of a wire-wound grid with its central longitudinalaxis at an acute angle with respect to the primary electrontrajectories.

2. An electron multiplier tube, comprising means to develop a beam ofprimary electrons, a secondary electron collector, and a dynode uponwhich said primary electrons impinge to release secondary electrons,said dynode being in the form of a wire-wound grid disposed with itscentral longitudinal axis at an acute angle with respect to the angle ofincidence of the primary electrons, said grid having its wire turns ofsumcient cross-section to provide a barrier between the primaryelectrons and the collector.

3. An electron tube according to claim 1, in which said collector isinterior of said dynode.

4. An electron tube according to claim 1, in which said collector isexternal of said dynode.

5. An electron multiplier tube, comprising a secondary electroncollector and a dynode grid in co-axial relation, a cathode for emittingprimary electrons mounted in spaced and end-on relation with respect tosaid dynode and collector, and means in the form of a primary electrondeflector located between the cathode and the dynode to cause theprimary electrons from said cathode to strike said dynode at an acuteangle which is related to the cross-sectional thickness of the dynodegrid wires whereby said wires act as a barrier against primary electronsreaching said collector.

6. An electron multiplier tube according to claim 5, in which a bailiemember is located between the cathode and dynode grid to protect thedynode grid from the direct heat of the cathode and to protect itagainst the deposition of particles emanating from the cathode.

'7. An electron multiplier tube, comprising a secondary electroncollector, a dynode, said dynode having a plurality of spaced wiremembers, means to develop a beam of primary electrons, and means tocause said primary electrons to impinge upon said members at an acuteangle and thereby to shield said collector from said primary electrons,the last-mentioned means including a deflector for the primaryelectrons.

8. An electron multiplier tube, comprising a secondary electroncollector, a dynode, said dynode having a plurality of spaced wiremembers, means to develop a beam of primary electrons, and means tocause said primary electrons to impinge upon said members at an acuteangle and thereby to shield said collector from said primary electrons,the last-mentioned means including an electron bafiie and an electrondeflector between which the primary electrons are constrained to pass.

9. An electron multiplier tube, comprising a secondary electroncollector, a dynode, said dynode having a plurality of spaced wiremembers, means to develop a beam of primary electrons, and means tocause said primary electrons to impinge upon said members at an acuteangle and thereby to shield said collector from said primary electrons,said dynode being in the form of a wire-wound grid having its centrallongitudinal axis facing the primary electron developing means.

10. An electron multiplier tube, comprising a secondary electroncollector, a dynode, said dynode having a plurality of spaced wiremembers, means to develop a beam of primary electrons, and means tocause said primary electrons to impinge upon said members at an acuteangle and thereby to shield said collector from said primary electrons,said dynode being in the form of a, helically-wound grid, and saidcollector being in the form of a metal plate which is surrounded by saidgrid.

11. An electron multiplier tube, comprising a secondary electroncollector, a dynode, said dynode having a plurality of spaced wiremembers, means to develop a beam of primary electrons, and means tocause said primary electrons to impinge upon said members at an acuteangle and thereby to shield said collector from said primary electrons,said dynode being in the form of a helically-wound grid, and saidcollector being in the form of a tubular conductive member surroundingsaid grid.

12. An electron multiplier tube, comprising a secondary electroncollector, a dynode, said dynode having a, plurality of spaced wiremembers, means to develop a beam of primary electrons, and means tocause said primary electrons to impinge upon said members at an acuteangle and thereby to shield said collector from said primary electrons,said collector comprising a series of spaced conductor strips mounted inregistry with the spaces between said wire members.

CARL F. MILLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,748,386 Loewe Feb. 25, 19302,233,878 Snyder Mar. 4, 1941

